> Yes it is a big hurdle. However, I think content discovery is generally a big part of any content platform, way broader than discovering "who have reacted to my content". Now if you want to solve the problem of content discovery in a broader sense, then you have already fixed this particular shortcoming of pull-model as well.

Right but I don't think as a general case finding all RSS feeds on the internet that satisfy a certain criteria, like publishing a hashtag or responding to a particular post, is a problem that can actually be solved in a principled way, because a fundamental limitation of the pull methodology is that you have to know the list of places you are checking beforehand, you can't get content from somewhere you didn't know about prior. The only way to solve this would be to have some kind of crawling and indexing system that regularly crawls the entire internet looking for these expanded RSS feeds and then categorized them according to various criteria in order to poll them. And that is both a very high technical investment and has a lot of limitations itself. So in the end it seems like you haven't really actually distributed the work of a social media system more equally after all, you've just inverted who is doing the work, going from a Federated set of servers that do all the work pushing content everywhere to a Federated set of servers that do all the work pulling content from places.